Method for the production of 4,4′-[1-(trifluoromethyl)alkylidene]-bis-(2,6-diphenylphenols)

ABSTRACT

The present invention relates to a process for preparing 4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenols), in particular for preparing 4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol), which comprises the self-condensation of cyclohexanone in the presence of a basic catalyst to form tricyclic condensation products, dehydrogenation of the resulting tricyclic condensation products in the presence of a supported transition metal catalyst in the condensed phase to form 2,6-diphenylphenol and reaction of the 2,6-diphenylphenol with a trifluoromethyl ketone. The invention further provides an improved process for preparing 2,6-diphenylphenol by aldol self-condensation of cyclohexanone.

RELATED APPLICATIONS

This application is a national stage application (under 35 U.S.C. §371)of PCT/EP2008/067686, filed Dec. 17, 2008, which claims benefit ofEuropean Application No. 07123368.8, filed Dec. 17, 2007.

The present invention relates to a process for preparing4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenols), inparticular for preparing4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol), whichcomprises the self-condensation of cyclohexanone in the presence of abasic catalyst to form tricyclic condensation products, dehydrogenationof the resulting tricyclic condensation products in the presence of asupported transition metal catalyst in the condensed phase to form2,6-diphenylphenol and reaction of the 2,6-diphenylphenol with atrifluoromethyl ketone. The invention further provides an improvedprocess for preparing 2,6-diphenylphenol by aldol self-condensation ofcyclohexanone and subsequent dehydrogenation.

4,4′-[1-(Trifluoromethyl)ethylidene]bis(2,6-diphenylphenol) and4,4′-[1,1-bis(trifluoromethyl)methylidene]bis(2,6-diphenylphenol) areknown from U.S. Pat. No. 3,739,035 and are described as valuablestarting materials for preparing polycarbonates or polyesters. They areprepared by reacting 2,6-diphenylphenol with in each case large excessesof gaseous hexafluoroacetone or 1,1,1-trifluoroacetone inmethanesulfonic acid.

The compounds mentioned are also important starting materials forpreparing bis(diarylphenoxy)aluminum compounds as are described in WO2006/092433.

DE 1 643 402 relates to a process for preparing 2,6-diphenylphenol byself-condensation of cyclohexanone to form tricyclic condensationproducts and subsequent dehydrogenation of these. Here, theself-condensation of cyclohexanone is carried out under solvent-freeconditions at temperatures of up to 200° C. in the presence of a strongbase, preferably aqueous solutions of sodium hydroxide or potassiumhydroxide, as catalyst. The dehydrogenation of the tricycliccondensation products obtained in admixture with bicyclic condensationproducts which is to be carried out in the second step is carried out inthe presence of a dehydrogenation catalyst at a temperature of up to350° C., preferably from 300 to 350° C. Suitable dehydrogenationcatalysts described are supported platinum, palladium, nickel, rutheniumand rhodium catalysts.

DE 1 643 403 discloses a process for crystallizing 2,6-diphenylphenolfrom a mixture comprising 2,6-diphenylphenol together with at least onefurther phenol which has an aliphatic 6-membered ring instead of aphenyl ring in the 2 or 6 position. For this purpose, the mixtures aredissolved in a mixture of from 75 to 99% by weight of an aliphaticsolvent with from 1 to 25% by weight of an aromatic solvent and thetemperature of the solution is reduced to a point below thecrystallization temperature of 2,6-diphenylphenol.

DE 2 211 721 relates to a process for preparing orthophenylphenol,wherein the product of the bimolecular dehydration condensation ofcyclohexanone is introduced into a bed of a catalyst supported on aninactive support and the condensate is subjected to dehydrogenation atfrom 230 to 520° C. in the presence of an inert gas. The document alsodiscloses catalysts which are suitable for carrying out the process andcomprise one or more of the elements palladium, platinum, iridium andrhodium and may further comprise an alkali.

Proceeding from this prior art, it was an object of the presentinvention to provide a process which makes it possible to prepare4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenols) and2,6-diphenylphenol in a particularly economical manner, i.e. with a veryhigh yield of the desired compounds and with very little formation ofundesirable by-products which may, if appropriate, have to be separatedoff in a complicated fashion and be disposed of or recirculated, and ina manner which is very advantageous from a process engineering point ofview.

The object was achieved according to the invention by provision of aprocess for preparing4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenols) of theformula (I)

where the radical

R is unbranched or branched C₁-C₆-alkyl or C₁-C₆-perfluoroalkyl,

which comprises the process steps

-   -   a) reaction of cyclohexanone in the presence of a basic catalyst        to form a reaction mixture comprising the tricyclic condensation        products of the formula (IIa), (IIb) and/or (IIc)

-   -    and water,    -   b) separation of a mixture of the tricyclic condensation        products comprising the compounds of the formulae (IIa), (IIb)        and/or (IIc) from the reaction mixture formed in step a),    -   c) dehydrogenation of the tricyclic condensation products        comprising the compounds of the formulae (IIa), (IIb) and/or        (IIc) obtained in step b) in the presence of a supported        transition metal catalyst in the condensed phase to form a        reaction mixture comprising 2,6-diphenylphenol of the formula        (III),

-   -   d) separation of 2,6-diphenylphenol of the formula (III) from        the reaction mixture formed in step c) and    -   e) reaction of the 2,6-diphenylphenol of the formula (III)        obtained in step d) with a trifluoromethyl ketone of the formula        (IV)

-   -    where the radical R is as defined for formula (I), in the        presence of a strong organic acid to form the        4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenol) of        the formula (I).

The process of the invention is suitable for preparing4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenols) of theformula (I)

where the radical R is unbranched or branched C₁-C₆-alkyl orC₁-C₆-perfluoroalkyl. Here, the term branched or unbranched C₁-C₆-alkylrefers to branched or unbranched alkyl radicals having from 1 to 6carbon atoms, for example methyl, ethyl, propyl, isopropyl, butyl,sec-butyl, tert-butyl, pentyl or hexyl. Preferred C₁-C₆-alkyl radicalsare methyl, ethyl, isopropyl, particularly preferably methyl. The termbranched or unbranched C₁-C₆-perfluoroalkyl refers to branched orunbranched perfluoroalkyl radicals, i.e. alkyl radicals in which allhydrogen atoms have been replaced by fluorine atoms, having from 1 to 6carbon atoms, for example trifluoromethyl, pentafluoroethyl,heptafluoropropyl, heptafluoroisopropyl, nonafluorobutyl. PreferredC₁-C₆-perfluoroalkyl radicals are trifluoromethyl, pentafluoroethyl,heptafluoroisopropyl, particularly preferably trifluoromethyl. Possibleparticularly preferred process products are accordingly4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol) of theformula (Ia)

and 4,4′-[1,1-(bistrifluoromethyl)methylidene]bis(2,6-diphenylphenol) ofthe formula (Ib)

A process product which is very particularly preferred according to theinvention is 4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol)of the formula (Ia).

The process of the invention comprises the process steps a) to e). Inprocess step a) of the process of the invention, a reaction ofcyclohexanone in the presence of a basic catalyst is carried out to forma reaction mixture comprising the tricyclic condensation products of theformula (IIa), (IIb) and/or (IIc)

and water. Accordingly, cyclohexanone serves as starting material forcarrying out the process of the invention. This can be used incommercial purity, i.e. without particular purity requirements,production process or nature, usually in a purity of about 95% by weightor above, preferably 99% by weight or above.

The reaction of cyclohexanone according to step a) of the process of theinvention is an intermolecular self-condensation of 3 molecules ofcyclohexanone in an aldol condensation (aldol addition with subsequentelimination of water), as is known per se to those skilled in the art.This forms product mixtures of tricyclic cyclohexanones which comprisethe compounds of the formulae (IIa), (IIb) and/or (IIc) depicted above.The mixtures mentioned can comprise one, two or all three of thecompounds (IIa), (IIb) and (IIc) mentioned and may additionally comprisefurther isomers of the compounds mentioned, for example those in whichan ethylenic double bond is localized in the cyclohexanone ring of themolecule. It is usual for all three tricyclic ketones of the formulae(IIa), (IIb) and (IIc) to be present in the product mixtures mentioned.

Bicyclic cyclohexanones, especially those of the formulae (Va) and/or(Vb)

are generally also formed as undesirable by-products of theself-condensation of cyclohexanone to be carried out in step a) of theprocess of the invention. However, these can, as described below understep b) of the process of the invention, be separated off from thetricyclic reaction products of the formulae (IIa), (IIb) and/or (IIc),preferably by distillation, and, if desired, be recirculated to thereaction in process step a).

The reaction in process step a) is carried out in the presence of abasic catalyst, preferably in the presence of an inorganic, especiallystrongly basic, catalyst. As basic or strongly basic, in particularinorganic, catalysts or bases, mention may be made of those which areable to convert cyclohexanone at least partly into the correspondingenolate anion by deprotonation. The reaction in process step a) ispreferably carried out in the presence of a strong base, particularlypreferably a base which has a pKb of less than 4. As preferred strongbases for this purpose, mention may be made of the hydroxides,alkoxides, hydrides, amides or carbonates of alkali metals or alkalineearth metals, for example lithium, sodium, potassium, calcium and bariumhydroxide, sodium ethoxide, sodium methoxide, potassium tert-butoxide,sodium and potassium hydride, lithium diisopropylamide and also lithium,sodium, potassium, calcium and barium carbonate. Particularly preferredstrong bases are the hydroxides and carbonates of the alkali metals oralkaline earth metals, very particularly preferably the hydroxides ofthe alkali metals. The compounds mentioned can be used in pure form orin the form of mixtures with one another or in the form of mixtures withother bases. They can be used in solid or dissolved form, preferably inthe form of aqueous solutions.

The amount of basic catalyst to be used in process step a) is notcritical and can be varied within a wide range. However, taking intoaccount the economic aspect, it is advantageous to use the catalyst inthe smallest possible amount, preferably in an amount of up to 20 mol %,particularly preferably up to 10 mol % and very particularly preferablyup to 5 mol %, in each case based on the base equivalents and the amountof cyclohexanone used.

In process step a) of the process of the invention, preference is givento using an aqueous solution of an alkali metal hydroxide or alkalineearth metal hydroxide, particularly preferably an aqueous solution ofsodium hydroxide, as basic catalyst. If the base selected is used in theform of a solution, preferably in the form of an aqueous solution, thepreferred concentration range of these solutions is from about 5 toabout 50% by weight (based on the finished solution), particularlypreferably from about 25 to about 50% by weight.

The self-condensation of cyclohexanone to be carried out in process stepa) can be carried out in a wide temperature range, usually attemperatures of from about 70° C. to about 200° C. A preferredtemperature range for carrying out process step a) of the process of theinvention is the range from 90 to 180° C.

During the course of the self-condensation of the cyclohexanone used,i.e. as conversion progresses, the dimeric, bicyclic condensationproducts of the formulae (Va) and (Vb) are firstly formed as primarycondensation products from the reaction of two molecules ofcyclohexanone. These have a boiling point higher than that ofcyclohexanone itself and have to react with a further molecule ofcyclohexanone to form the desired tricyclic condensation products of theformulae (IIa), (IIb) and/or (IIc).

In an embodiment of the process of the invention which is particularlypreferred according to the invention, the reaction according to processstep a) is carried out in the presence of a solvent (other thancyclohexanone) or solvent mixture which forms an azeotrope with water.Preferred “solvents which form an azeotrope with water” are solvents,preferably organic solvents, which are inert under the reactionconditions and have a boiling point at atmospheric pressure of fromabout 100° C. to about 200° C., preferably in the range from 100° C. to150° C., particularly preferably in the range from 110° C. to 140° C.and very particularly preferably in the range from 130° C. to 140° C.,and are different from cyclohexanone. Particular preference is given tothose organic solvents which form an azeotrope with water which has aboiling point lower than that of cyclohexanone, i.e. less than 155° C.,and a boiling point lower than that of the respective solvent itself(low-boiling azeotrope). Very particular preference is given to thosesolvents or solvent mixtures whose azeotropic boiling point is below theazeotropic boiling point of cyclohexanone of 95° C. To ensure asatisfactory reaction rate, it is advantageous for the azeotropicboiling point of the solvent or solvent mixture selected to be as highas possible, preferably 70° C. or above, particularly preferably 80° C.or above. In process step a) of the process of the invention, solventswhich can particularly preferably be used according to the inventionaccordingly have an azeotropic boiling point in the range from 70° C. to95° C., preferably from 80° C. to 95° C., particularly preferably up to<95° C., for example toluene, xylene and ethylbenzene or mixturesthereof, preferably xylene. The abovementioned “solvent which forms anazeotrope with water” can therefore also be referred to as an entrainer.

The solvents mentioned can be used as such or in the form of mixtures oftwo or more different solvents. Preference is given to using only onesolvent, preferably a solvent which forms an azeotrope as describedabove with water, in process step a) of the process of the invention.

In another preferred embodiment, the process of the invention is carriedout so that the water formed in process step a) by aldolself-condensation of cyclohexanone is separated from the reactionmixture by distillation in the form of an azeotrope with the solventused during the reaction. The removal of the water of reaction formed inthe aldol self-condensation of cyclohexanone and any water added in theform of an aqueous solution of the basic catalyst can be carried out byazeotropic distillation methods known per se to those skilled in the artusing apparatuses which are likewise known for the separation or removalof water from a reaction mixture, for example a water separator. Thewater can be separated off completely or largely completely or onlypartly. However, preference is given to separating off thestoichiometrically expected amount of water to be formed (and also anyamount of water added with the catalyst) as completely as possible inorder to aid the desired formation of the above-mentioned tricyclicreaction products.

The amount of solvent which forms an azeotrope with water to be used inthis preferred embodiment can be selected within a wide range and can bedependent on various factors, in particular on the choice of thespecific solvent or solvent mixture used and on the process or apparatusused for separating off or removing the water. The selected solvent isusually, taking account of economic factors, used in an amount of from 5to 100% by weight, preferably from 10 to 60% by weight and particularlypreferably from 15 to 40% by weight, of the amount of cyclohexanoneused.

This gives a reaction mixture which comprises, apart from the basiccatalyst used, essentially the desired tricyclic ketones of the formulae(IIa), (IIb) and/or (IIc) together with bicyclic condensation productsof the formula (Va) and/or (Vb) and unreacted cyclohexanone. Thereaction mixture obtained in this way can be processed further in thisform or firstly be worked up, for example by extractive processes withwhich those skilled in the art will be familiar. It is advantageousfirstly to carry out a neutralization of the basic catalyst by treatmentwith an acid.

In process step b) of the process of the invention, the tricycliccondensation products comprising the compounds of the formulae (IIa),(IIb) and/or (IIc) are separated off from the optionally worked-up andlargely neutralized reaction mixture formed in this way in process stepa). The separation can be effected by methods which appear suitable tothose skilled in the art, for example by chromatography or distillation.The separation of the tricyclic reaction products of the formulae IIa,IIb and/or IIc from the reaction mixture obtained in process step a), ifappropriate after neutralization and work-up by extraction, in processstep b) is preferably carried out in the form of a distillation.

The isolation of the tricyclic condensation products by distillation canbe carried out batchwise, semicontinuously or fully continuously.Preference is given to carrying out a batch or semicontinuousdistillation, particularly preferably a batch distillation. The designof the distillation column to be used does not have to meet anyparticular requirements. It can be advantageous to use packed columns,e.g. columns packed with suitable mesh packing, sheetmetal packing ordisordered beds of packing elements. The distillation is advantageouslycarried out under reduced pressure, preferably at a pressure at thebottom of from about 1 to about 100 mbar, particularly preferably fromabout 5 to about 30 mbar abs., and a pressure at the top of from about 1to about 100 mbar abs., particularly preferably from about 5 to about 20mbar abs. Accordingly, the temperature at the bottom is advantageouslyfrom about 200 to about 250° C., preferably from about 210 to about 230°C., and the temperature at the top is from about 190 to about 220° C.,preferably from about 200 to about 210° C. The tricyclic ketones of theformulae (IIa), (IIb) and/or (IIc) are obtained as high-boiling bottomproduct from which the lower-boiling components, in particular thebicyclic condensation products of the formulae (Va) and/or (Vb), aredistilled off as overhead product. These can, if desired, berecirculated as starting material to the aldol self-condensation ofcyclohexanone in process step a) of the process of the invention.

In process step c) of the process of the invention, a dehydrogenation ofthe tricyclic condensation products comprising the compounds of theformula (IIa), (IIb) and/or (IIc) obtained according to process step b)is carried out in the presence of a supported transition metal catalystin the condensed phase to form a reaction mixture comprising2,6-diphenylphenol of the formula (III)

The dehydrogenation step in process step c) of the process of theinvention is carried out in the condensed, i.e. liquid, phase. Here, themixture comprising the tricyclic ketones of the formulae (IIa), (IIb)and/or (IIc) to be reacted and the 2,6-diphenylphenol of the formula(III) obtained as dehydrogenation product and also any partiallydehydrogenated compounds obtained, for example2-cyclohexyl-6-phenylphenol, are present largely, i.e. predominantly, inliquid form. The dehydrogenation is usually carried out at elevatedtemperature, preferably at temperatures in the range from about 200° C.to about 300° C., i.e. at temperatures below the boiling point of thetricyclic starting materials mentioned or products of thedehydrogenation. The dehydrogenation is preferably carried out at atemperature in the range from 240 to 300° C., particularly preferably inthe range from 250 to 300° C.

Furthermore, the dehydrogenation in process step c) is carried out inthe presence of a supported transition metal catalyst. Suitablesupported transition metal catalysts are in principle all those whichare known to those skilled in the art as catalysts for suchdehydrogenation reactions to form aromatic systems, for example thosecomprising one or more of the transition metals palladium, platinum,nickel, ruthenium, rhodium on a suitable support. The dehydrogenation inprocess step c) is preferably carried out in the presence of a catalystcomprising palladium (Pd) and/or platinum (Pt) on a support. Thecatalysts which are preferably to be used in process step c) cancomprise the transition metals palladium and platinum eitherindividually or in the form of a mixture with one another, ifappropriate together with further metals. Preference is given to usingcatalysts which comprise palladium as catalytically active metal. Themetals mentioned are used in supported form, i.e. in a form in whichthey have been applied to materials which are known per se to thoseskilled in the art as support materials. As suitable support materials,mention may be made by way of example of: silica gel (SiO₂), aluminumoxide (Al₂O₃), carbon, activated carbon, zirconium oxide (ZrO₂),titanium dioxide (TiO₂). In a preferred embodiment, the dehydrogenationin process step c) of the process of the invention is carried out in thepresence of a Pd catalyst supported on Al₂O₃ or on a carbon support suchas activated carbon. Here, the Al₂O₃ can be used in the form of γ-Al₂O₃(gamma-Al₂O₃) or in the form of δ-Al₂O₃ (delta-Al₂O₃) or in the form ofθ-Al₂O₃ (theta-Al₂O₃) or in the form of δ/θ-Al₂O₃ (delta/theta-Al₂O₃) orin the form of α-Al₂O₃ (alpha -Al₂O₃), as described, for example, inHollemann Wiberg, Lehrbuch der Anorganischen Chemie, 102nd edition, deGruyter, 2007, page 1161. Preference is given to using γ-Al₂O₃(gamma-Al₂O₃) as support. A supported catalyst which is particularlypreferred for the purposes of the present invention is therefore Pd onγ-Al₂O₃ (gamma-Al₂O₃).

The catalytically active metals, preferably palladium and/or platinum,are usually present in the supported catalyst in a proportion by weightof from about 0.1 to about 20% by weight, preferably from about 0.1 to10% by weight (in each case based on the finished catalyst). They areusually, depending on the type of catalyst used, used in an amount offrom 1 to 40% by weight, preferably from 1 to 35% by weight, based onthe weight of the mixture of tricyclic ketones to be dehydrogenated.

The supported transition metal catalyst to be used according to theinvention can be used in a wide variety of forms known to those skilledin the art, for example in the form of spheres, extrudates or as powder.

In a further preferred embodiment, the dehydrogenation in process stepc) can be carried out in the presence of hydroxides or carbonates ofalkali metals or alkaline earth metals, for example in the presence oflithium, sodium, potassium, calcium or barium hydroxide and/or lithium,sodium, potassium, calcium or barium carbonate, in addition to thesupported transition metal catalyst used. The basic compounds mentionedcan, depending on the type of compound or compounds used, be used in anamount of usually from 3 to 20% by weight based on the supportedcatalyst used. As an alternative, it is also possible to use supports orsupported catalysts which have been treated with the abovementionedalkali metal or alkaline earth metal hydroxides or carbonates.

The dehydrogenation in process step c) generally proceeds quickly and atthe reaction temperatures mentioned is usually substantially completeafter about 24 h, often after about 12 h or less. The dehydrogenationgives a reaction mixture which comprises the fully dehydrogenatedcompound 2,6-diphenylphenol of the formula (III), generally togetherwith tricyclic ketones which have not been dehydrogenated or been onlypartially dehydrogenated.

The heterogeneous dehydrogenation catalysts described above can beseparated off by methods with which those skilled in the art arefamiliar, for example by filtration or centrifugation, preferably byfiltration. When the above-described supported transition metalcatalysts are used, in particular when the abovementioned catalystcomprising palladium (Pd) and/or platinum (Pt) on a support is used, ithas been found that the catalysts separated off after the reaction inprocess step c) generally still have a high activity. They can thereforeadvantageously be reused, preferably in further reactions as per processstep c). In a preferred embodiment of the process of the invention, thecatalyst used in process step c) is therefore separated off from thereaction mixture after the reaction has been carried out and is reusedin one or more further reactions as per process step c).

The catalyst which has been recovered in each case can in principle beused for as long and as often as it still retains the desired activity.This generally depends on the catalyst selected in each case, on thestarting materials selected and on the reaction conditions. When acatalyst comprising palladium (Pd) and/or platinum (Pt), especiallypalladium (Pd) on a support is used, this can usually be recirculated,i.e. reused, up to ten or more times, but at least up to five times orup to four times, without appreciable decreases in activity orselectivity in the dehydrogenation reaction occurring.

The above-described addition of hydroxides or carbonates of alkalimetals or alkaline earth metals in process step c), which is preferredaccording to the invention, can also have an advantageous effect on theactivity, operating life or reusability of the supported transitionmetal catalyst used in each case. The addition of alkali metal oralkaline earth metal carbonates, preferably sodium and/or potassiumcarbonate and very particularly preferably potassium carbonate (K₂CO₃),in particular, can lead to an increase in activity and thus to improvedreusability of the particular supported catalyst used. This effect isparticularly pronounced in reactions using supported palladiumcatalysts, especially in reactions using the particularly preferred Pdon γ-Al₂O₃ (gamma-Al₂O₃) as catalyst. In a particularly preferredembodiment, step c) of the process of the invention is accordinglycarried out in the presence of Pd on γ-Al₂O₃ (gamma-Al₂O₃) as supportedtransition metal catalyst and in the presence of an alkali metalcarbonate, preferably in the presence of potassium carbonate.

In process step d) of the process of the invention, a separation of2,6-diphenylphenol of the formula (III) from the reaction mixture formedin process step c) is carried out. The separation according to processstep d) can in principle be carried out by means of customary methodsfor effecting separation of materials, for example distillation,chromatography or crystallization. It has been found to be advantageousto separate 2,6-diphenylphenol from the undesirable undehydrogenated oronly partially dehydrogenated tricyclic ketones by crystallization.Solvents which have been found to be suitable for this purpose are lowerhydrocarbons having up to 8 carbon atoms, for example pentane, hexane,cyclohexane, heptane, octane, toluene, xylene, if appropriate inadmixture with lower aliphatic alcohols having from 1 to 4 carbon atoms,e.g. methanol, ethanol, propanol, isopropanol or butanol, or withketones, ethers or esters having up to 5 carbon atoms, for exampleacetone, tert-butyl methyl ether or ethyl acetate. It has been found tobe particularly advantageous to carry out the isolation of2,6-diphenylphenol according to process step d) in the form of acrystallization from heptane or a heptane-comprising solvent mixture.Pure heptane or a mixture of heptane and isopropanol in a volume ratioof from about 20:1 to about 30:1 has been found to be very particularlyuseful as solvent or solvent combination. The term heptane encompassesboth n-heptane and also isomers thereof, for example 2-methylhexane,3-methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane,2,4-dimethylpentane, 3,3-dimethylpentane, 3-ethylpentane,2,2,3-trimethylbutane or mixtures thereof.

The 2,6 diphenylphenol of the formula (III) obtained by theabove-described crystallization can subsequently be separated off fromthe mother liquor in the customary manner, preferably by filtration orcentrifugation.

In this way, 2,6-diphenylphenol of the formula (III) can be obtained inpure form, i.e. in a purity of at least 98% by weight, often at least99% by weight. This material is low in undesirable undehydrogenated oronly partially dehydrogenated tricyclic ketones which would be separatedoff only with difficulty in further process steps or reactions and wouldlead to undesirable product mixtures and secondary reactions.

In process step e) of the process of the invention, the2,6-diphenylphenol of the formula (III) obtained in process step d) isreacted with a trifluoromethyl ketone of the formula (IV)

where the radical R is as defined for formula (I), in the presence of astrong organic acid to form the4,4-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenol) of theformula (I).

Depending on the desired target compound, the 2,6-diphenylphenolprepared according to process steps a) to d) is reacted in process stepe) with a trifluoromethyl ketone of the formula (IV), where the radicalR can be C₁-C₆-alkyl or C₁-C₆-perfluoroalkyl as described above for thecompounds of the formula (I). To prepare the process products of theformulae (Ia) and (Ib) which are particularly preferred according to theinvention, the 2,6-diphenylphenol obtained in process step d) isaccordingly reacted either with 1,1,1-trifluoroacetone of the formula(IVa)

or with hexafluoroacetone of the formula (IVb)

Both reagents can be used in commercial form without any particularrequirements in terms of purity or production process. Hexafluoroacetoneof the formula (IVb) is preferably passed in gaseous form into thereaction mixture.

The chosen trifluoromethyl ketone is advantageously used according tothe stoichiometry of the reaction, preferably in a slight excess. Thecompounds 2,6-diphenylphenol and the trifluoromethyl ketone of theformula (IV) selected are usually used in a molar ratio of from about1:1 to about 2:1, preferably from about 2.0:1.2 to about 2.0:1.1.

The reaction in process step e) is carried out in the presence of astrong organic acid, preferably an organic acid having a pKa of up to 2,particularly preferably a pKa in the range from −1 to 2, veryparticularly preferably a pKa in the range from 1 to 2. As preferredorganic acids which can be used in process step e), mention may be madeof sulfonic acids, especially alkylsulfonic or phenylsulfonic acids.Preferred sulfonic acids are, for example: methanesulfonic acid,trifluoromethanesulfonic acid, benzenesulfonic acid,para-toluene-sulfonic acid, particularly preferably methanesulfonic acidor trifluoromethanesulfonic acid and very particularly preferablymethanesulfonic acid.

The strong organic acid selected, preferably methanesulfonic acid ortrifluoromethanesulfonic acid, particularly preferably methanesulfonicacid, is used in undiluted form (100% strength) in a preferredembodiment. The acid is usually used in a significant excess over theamount of 2,6-diphenylphenol to be reacted. In general, with a view toeconomic aspects, a weight ratio of the acid selected to2,6-diphenylphenol of from about 10:1 to about 30:1, preferably fromabout 10:1 to about 20:1, is selected.

To carry out the reaction according to process step e), the selectedreagents can be brought into contact with one another in any order,usually at temperatures in the range from 0 to 100° C. The reactionaccording to process step e) is preferably carried out at a temperaturein the range from 10 to 60° C., particularly preferably in the rangefrom 20 to 50° C. The reaction is then usually largely complete afterreaction times of from 10 to 24 hours.

The target compound of the formula (I), which is generally obtained insolid form, can be isolated from the resulting reaction mixture byconventional separation methods, preferably by filtration or preferablyby extraction, preferably by extraction with toluene, xylene orethylbenzene or mixtures thereof. In a preferred embodiment, the processof the invention is carried out with the4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenols) of theformula (I) formed in process step e) being separated off from theresulting reaction mixture by extraction. An extractant which isparticularly preferred in this embodiment is toluene. In this way, theorganic acid used, preferably the methanesulfonic acid ortrifluoromethanesulfonic acid used, can be recovered and reused ifdesired, preferably in a further reaction according to process step e)of the process of the invention. The extractant used, preferablytoluene, which is dissolved in the recovered methanesulfonic acid afterthe extraction to be carried out in this preferred embodiment can beseparated off by distillation in order to avoid secondary reactions with1,1,1-trifluoroacetone and toluene.

The process of the invention therefore comprises, in a further optionalprocess step f), the separation of the target compound of the formula(I) from the reaction mixture obtained in process step e). The desiredtarget compound is usually obtained in a purity of 95% by weight orabove, preferably in a purity of 97% by weight or above.

The process of the invention therefore offers an effective route to thedesired target compounds of the formula (I), in particular the compoundsof the formulae (Ia) and (Ib), which are preferred target compounds forthe purposes of the present invention. The process of the inventionmakes it possible to prepare the abovementioned compounds in a hightotal yield and high purity.

In a further aspect, the present invention provides a process forpreparing 2,6-diphenylphenol of the formula (III)

which comprises the steps

-   -   i) reaction of cyclohexanone in the presence of a basic catalyst        to form a reaction mixture comprising the tricyclic condensation        products of the formula (IIa), (IIb) and/or (IIc)

-   -    and water in the presence of a solvent or solvent mixture other        than cyclohexanone which forms an azeotrope with water, with the        water formed being separated off from the reaction mixture by        distillation in the form of an azeotrope with the solvent used        during the reaction,    -   ii) separation of a mixture of the tricyclic condensation        products comprising the compounds of the formulae (IIa), (IIb)        and/or (IIc) from the reaction mixture formed in step i) and    -   iii) dehydrogenation of the tricyclic condensation products        comprising the compounds of the formulae (IIa), (IIb) and/or        (IIc) obtained in step ii) in the presence of a supported        transition metal catalyst in the condensed phase to form a        reaction mixture comprising 2,6-diphenylphenol of the formula        (III)

This aspect of the present invention accordingly concerns a process forpreparing 2,6-diphenylphenol which corresponds to process steps a) to c)of the above-described process, with the self-condensation ofcyclohexanone being carried out in the presence of a basic catalystaccording to process step i) in the presence of a solvent or solventmixture which forms an azeotrope with water (and is different fromcyclohexanone) and the water formed being separated off from thereaction mixture by distillation in the form of an azeotrope with thesolvent used during the reaction.

The term “solvent which forms an azeotrope with water” can have the samegeneral and preferred meanings as described above under process step a).Accordingly, the term “solvents which form an azeotrope with water” asused for the purposes of this aspect of the present invention, too,refers to preferably organic solvents which are inert under the reactionconditions and have a boiling point at atmospheric pressure of fromabout 100° C. to about 200° C., preferably in the range from 100 to 150°C., particularly preferably in the range from 110 to 140° C. and veryparticularly preferably in the range from 130 to 140° C., and aredifferent from cyclohexanone. Particular preference is given to thoseorganic solvents which together with water form an azeotrope which has aboiling point lower than that of cyclohexanone, i.e. lower than 155° C.,and a boiling point lower than the respective solvent itself(low-boiling azeotrope). Among these, very particular preference isgiven to solvents or solvent mixtures whose azeotropic boiling point isbelow the azeotropic boiling point of cyclohexanone of 95° C. To ensurea satisfactory reaction rate, it is advantageous for the azeotropicboiling point of the solvent or solvent mixture selected to be as highas possible, preferably 70° C. or above, particularly preferably 80° C.or above. Solvents which are particularly preferably used according tothe invention in process step a) of the process of the inventionaccordingly have an azeotropic boiling point in the range from 70° C. to95° C., preferably from 80° C. to 95° C., particularly preferably up to<95° C., for example toluene, xylene and ethylbenzene or mixturesthereof, preferably xylene. The “solvent which forms an azeotrope withwater” mentioned can therefore also be referred to as an entrainer.

The solvents mentioned can be used as such or in the form of mixtures oftwo or more different solvents. Preference is given to using only onesolvent, preferably one which together with water forms an azeotrope asdescribed above, in process step i) of the process of the invention.

According to this aspect of the present invention, process step i) ofthe process of the invention is carried out so that the water formed byaldol self-condensation of cyclohexanone is separated off from thereaction mixture by distillation in the form of an azeotrope with thesolvent used during the reaction. The removal of the water of reactionformed in the aldol self-condensation of cyclohexanone and, ifappropriate, the water added in the form of an aqueous solution of thebasic catalyst can be effected by the azeotropic distillation methodsknown per se to those skilled in the art using likewise knownapparatuses for separating off or removing water from a reactionmixture, for example a water separator. The water can be removedcompletely or largely completely or only partly. However, preference isgiven to separating off the stoichiometrically expected amount of waterto be formed (and any amount of water added with the catalyst) to a verysubstantial extent in order to aid the desired formation of thetricyclic reaction products mentioned.

The amount of the solvent which forms an azeotrope with water to be usedaccording to this aspect of the present invention can be selected withina wide range and can depend on various factors, in particular on thechoice of the particular solvent or solvent mixture used and on theprocess or the apparatus used for separating off or removing the water.The solvent selected is usually, taking into account economic factors,used in an amount, based on the amount of cyclohexanone used, of from 5to 100% by weight, preferably from 10 to 60% by weight and particularlypreferably from 15 to 40% by weight.

As regards the basic catalysts to be used in process step i) and furtherfeatures of this process step, reference is made to the entirety of theabove description of process step a) including all preferred embodimentsand their combinations.

Accordingly, the reaction in process step i) is generally carried out inthe presence of a basic catalyst, preferably in the presence of aninorganic, in particular strongly basic catalyst. As basic or stronglybasic, in particular inorganic catalysts or bases, mention may be madeof those which are able to convert cyclohexanone at least partly intothe corresponding enolate anion by deprotonation. The reaction inprocess step i) is preferably carried out in the presence of a strongbase, particularly preferably a base which has a pKb of less than 4. Aspreferred strong bases for this purpose, mention may be made of thehydroxides, alkoxides, hydrides, amides or carbonates of alkali metalsor alkaline earth metals, for example lithium, sodium, potassium,calcium and barium hydroxide, sodium ethoxide, sodium methoxide,potassium tert-butoxide, sodium and potassium hydride, lithiumdiisopropylamide and also lithium, sodium, potassium, calcium and bariumcarbonate. Particularly preferred strong bases are the hydroxides andcarbonates of the alkali metals or alkaline earth metals, veryparticularly preferably the hydroxides of the alkali metals. Thecompounds mentioned can be used in pure form or in the form of mixtureswith one another or in the form of mixtures with other bases. They canbe used in solid or dissolved form, preferably in the form of aqueoussolutions.

In process step i) of the process of the invention, too, preference isgiven to using an aqueous solution of an alkali metal or alkaline earthmetal hydroxide, particularly preferably an aqueous solution of sodiumhydroxide, as basic catalyst. If the base selected is used in the formof a solution, preferably in the form of an aqueous solution, thepreferred concentration range of the solutions is from about 5 to about50% by weight (based on the finished solution), particularly preferablyfrom about 25 to about 50% by weight.

Process steps ii) and iii) of the process for preparing2,6-diphenylphenol described under this aspect of the present inventionalso correspond to process steps b) and c) of the above-describedprocess for preparing4,4′-[(1-trifluoromethyl)alkylidene]bis(2,6-diphenylphenols) of theformula (I). The separation to be carried out according to step ii) of amixture of the tricyclic condensation products comprising the compoundsof the formulae (IIa), (IIb) and/or (IIc) from the reaction mixtureformed in step i) and the dehydrogenation to be carried out according tostep iii) of the tricyclic condensation products comprising thecompounds of the formulae (IIa), (IIb) and/or (IIc) obtained in step ii)in the presence of a supported transition metal catalyst in thecondensed phase to form a 2,6-diphenylphenol of the formula (III) canaccordingly be carried out as described above for process steps b) andc), including all preferred embodiments and their combinations.Accordingly, process step iii) can also be carried out as describedabove in the presence of a supported transition metal catalyst. Here,suitable supported transition metal catalysts are in principle all thosewhich are known to those skilled in the art as catalysts for suchdehydrogenation reactions to form aromatic systems, for example thosecomprising one or more of the transition metals palladium, platinum,nickel, ruthenium, rhodium on a suitable support. The dehydrogenation inprocess step iii) is preferably carried out in the presence of acatalyst comprising palladium (Pd) and/or platinum (Pt) on a support.The catalysts which are preferably to be used in process step c) cancomprise the transition metals palladium and platinum, in each caseeither individually or in the form of a mixture with one another,optionally together with further metals. Preference is given to usingcatalysts which comprise palladium as catalytically active metal. Themetals mentioned are used in supported form, i.e. in a form in whichthey have been applied to materials which are known per se to thoseskilled in the art as support materials. As suitable support materials,mention may be made by way of example of: silica gel (SiO₂), aluminumoxide (Al₂O₃), carbon, activated carbon, zirconium oxide (ZrO₂),titanium dioxide (TiO₂). In a preferred embodiment, the dehydrogenationin process step iii) of the process of the invention is carried out inthe presence of a Pd catalyst supported on Al₂O₃ or on a carbon supportsuch as activated carbon. Here, the Al₂O₃ can be used in the form ofγ-Al₂O₃ (gamma-Al₂O₃) or in the form of δ-Al₂O₃ (delta-Al₂O₃) or in theform of θ-Al₂O₃ (theta-Al₂O₃) or in the form of δ/θ-Al₂O₃(delta/theta-Al₂O₃) or in the form of α-Al₂O₃ (alpha-Al₂O₃). Preferenceis given to using γ-Al₂O₃ (gamma-Al₂O₃) as support. A supported catalystwhich is particularly preferred for the purposes of the presentinvention is therefore Pd on γ-Al₂O₃ (gamma-Al₂O₃).

The catalytically active metals, preferably palladium and/or platinum,are usually present in the supported catalyst in a proportion by weightof from about 0.1 to about 20% by weight, preferably from about 0.1 to10% by weight (in each case based on the finished catalyst). They areusually used, depending on the type of catalyst used, in an amount offrom 1 to 40% by weight, preferably from 1 to 35% by weight, based onthe weight of the mixture of tricyclic ketones to be dehydrogenated.

In a further preferred embodiment, the dehydrogenation in process stepiii) can, in addition to the supported transition metal catalyst used,be carried out in the presence of hydroxides or carbonates of alkalimetals or alkaline earth metals, for example in the presence of lithium,sodium, potassium, calcium or barium hydroxide and/or lithium, sodium,potassium, calcium or barium carbonate. The basic compounds mentionedcan, depending on the type of compound or compounds used, be used in anamount of usually from 3 to 20% by weight, based on the supportedcatalyst used. As an alternative, supports or supported catalystspretreated with alkali metal or alkaline earth metal hydroxides orcarbonates as mentioned above can also be used.

Here, the catalyst recovered in each case can in principle be used forso long and as often as it still has the desired activity. Thisgenerally depends on the catalyst selected in each case, on the startingmaterials selected and on the reaction conditions. When a catalystcomprising palladium (Pd) and/or platinum (Pt), especially palladium(Pd), on a support is used, this can usually be recirculated, i.e.reused, up to about ten or more times, but at least up to five times orup to four times, without appreciable decreases in activity orselectivity occurring in the dehydrogenation reaction.

The above-described addition of hydroxides or carbonates of alkalimetals or alkaline earth metals in process step iii), which is preferredaccording to the invention, can also have an advantageous effect on theactivity, operating life or reusability of the supported transitionmetal catalyst used in each case. The addition of alkali metal oralkaline earth metal carbonates, preferably sodium and/or potassiumcarbonate and very particularly preferably potassium carbonate (K₂CO₃),in particular, can lead to an increase in activity and thus to improvedreusability of the supported catalyst used in each case. This effect isparticularly pronounced in reactions using supported palladiumcatalysts, especially in reactions using the particularly preferred Pdon γ-Al₂O₃ (gamma-Al₂O₃) as catalyst. In a particularly preferredembodiment, step iii) of the process of the invention is accordinglycarried out in the presence of Pd on γ-Al₂O₃ (gamma-Al₂O₃) as supportedtransition metal catalyst and in the presence of an alkali metalcarbonate, preferably in the presence of potassium carbonate.

If desired, an additional process step iv) involving the separation of2,6-diphenylphenol of the formula (III) from the reaction mixture formedin step iii) can be carried out after process step iii). This additionalprocess step iv) corresponds to process step d) of the above-describedprocess for preparing the compounds of the formula (I) and canaccordingly be carried out as described above for process step d),including all preferred embodiments and their combinations.

The following examples illustrate the invention without restricting itin any way:

Gas-chromatographic analyses were carried out by the following method:

30 m RTX 200, ID. 0.25 mm, FD: 0.50 μm; 200° C., 3° C./min-290° C.;t_(R) (min) t_(R) (bicyclic ketones of the formulae (Va, Vb)): 8.4, 8.8;t_(R) (tricyclic ketones of the formulae (IIa, IIb, IIc)): 17.1, 18.2,18.5; t_(R) (2-cyclohexyl-6-phenylphenol): 15.2; t_(R)(2,6-diphenylphenol): 18.7; t_(R) (α-phenyldibenzofuran): 21.6.Concentrations of the crude products obtained (% by weight) weredetermined by GC analysis using an internal standard.

HPLC analyses were carried out by the following method: CC250/4Nucleodur C18 Gravity, 5 μm; C: water-0.05% H₃PO₄; D: acetonitrile20:80; outlet: 93 bar, 25° C.; t_(R) (min) t_(R) (2,6-diphenylphenol):4.8; t_(R)(4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol)): 14.5.

EXAMPLE 1 Self-Condensation of Cyclohexanone

900 g (9.1 mol) of cyclohexanone together with 190 g of xylene wereplaced in a flask at room temperature. 33 g (0.21 mol) of NaOH solution(25%) were subsequently added. The reaction solution was stirred underreflux. Over a period of 7 hours, the temperature of the reactionmixture rose from 120 to 180° C., with 126 ml of water being removed bymeans of a water separator. The reaction solution was subsequentlycooled to room temperature.

To work up the reaction solution, 500 g of water were added to thissolution and the solution was neutralized with 11 g of H₃PO₄ (85%). Thephases were separated at 90° C. The organic phase was subsequentlywashed at 90° C. with 500 g of NaHCO₃ solution (2%). Phase separationwas likewise carried out at 90° C.

This gave 965 g of a crude product having the following composition:tricyclic ketones (formulae (IIa, IIb, IIc)): 48.3%; bicyclic ketones(formulae (Va, Vb)): 24.6% (in each case in GC-% by weight).

The crude product (965 g) was distilled batchwise in a laboratory glasscolumn provided with 1 m of Sulzer DX packing (number of theoreticalplates: about 20) and having an internal diameter of 50 mm and providedwith a still pot and a thin film evaporator with pumped circulation (0.1m²). The bicyclic ketones (formulae (Va, Vb)) were distilled off at 20mbar and a temperature at the top of 144° C. from the tricyclic ketones(formulae (IIa, IIb, IIc)) (temperature at the top: 212° C.; 20 mbar).The yield of bicyclic ketones of the formulae (Va, Vb) was 223 g (27%)and that of tricyclic ketones of the formulae (IIa, IIb, IIc) was 410 g(50% of theory; 96 GC-% by weight).

EXAMPLE 2 Recirculation of Bicyclic Ketones of the Formulae (Va, Vb)

360 g (3.0 mol) of cyclohexanone and 300 g (1.67 mol) of bicyclicketones of the formulae (Va, Vb) together with 140 g of xylene wereplaced in a flask at room temperature. 22.4 g (0.14 mol) of NaOHsolution (25%) were subsequently added. The reaction solution wasstirred under reflux. Over a period of 5 hours, the temperature rosefrom 120 to 180° C., with 62 ml of water being removed by means of awater separator. The red reaction solution was cooled to roomtemperature and a work-up as described in example 1 was carried out.

This gave 728 g of a crude product having the following composition:tricyclic ketones (formulae (IIa, IIb, IIc): 45.7%; bicyclic ketones(formulae (Va, Vb)): 27.0%; xylene: 14.5%; cyclohexanone: 3% (in eachcase in GC-% by weight).

EXAMPLES 3 to 5 Dehydrogenation of the Tricyclic Ketones of the Formulae(IIa, IIb, IIc) to Form 2,6-diphenylphenol of the Formula (III) EXAMPLE3

10 g of Pd/Al₂O₃ catalyst (0.5% by weight of palladium on a θ-Al₂O₃(theta-Al₂O₃) support in the form of spheres having a diameter of 3 mm)together with 30 g (0.11 mol) of the tricyclic ketones of the formulae(IIa, IIb, IIc) (97%) and 0.3 g of NaOH were placed in a flask at roomtemperature. The suspension was stirred at 290-300° C. for 4 hours.After the reaction mixture had cooled to room temperature, the reactionmixture was admixed with 200 ml of heptane. The reaction solution washeated to 90° C. and the catalyst was subsequently filtered off andwashed with 100 ml of heptane. The crude product was evaporated on arotary evaporator.

This gave a crude product having the following composition:2,6-diphenylphenol: 71.3%, tricyclic ketones of the formulae (IIa, IIb,IIc): 8.2% (in each case in GC-% by weight) and2-cyclohexyl-6-phenylphenol: 5.0 GC-% by area. The 2,6-diphenylphenolproduct was isolated by crystallization from heptane (120 ml) in a yieldof 62% (17.8 g, 97 GC-% by weight).

EXAMPLE 4

10 g of Pd/Al₂O₃ (0.72% by weight of palladium on a γ-Al₂O₃(gamma-Al₂O₃) support in the form of extrudates having a length of 4 mm)together with 30 g (0.11 mol) of the tricyclic ketones of the formulae(IIa, IIb, IIc) (97%) and 0.3 g of NaOH were placed in a flask at roomtemperature. The suspension was stirred at 290-300° C. for 8 hours. Thereaction mixture was cooled to 95° C., admixed with 200 ml of heptaneand a work-up as described in example 3 was carried out.

This gave a crude product having the following composition:2,6-diphenylphenol: 44.8%, tricyclic ketones of the formulae (IIa, IIb,IIc): 4.9% (in each case in GC-% by weight) and2-cyclohexyl-6-phenylphenol: 12.3 GC-% by area.

The 2,6-diphenylphenol product was isolated by crystallization fromheptane in a yield of 34% (9.5 g, 99 GC-% by area).

EXAMPLE 5

10 g of Pd/Al₂O₃ (0.72% by weight of palladium on a γ-Al₂O₃(gamma-Al₂O₃) support in the form of extrudates having a length of 4 mm)together with 30 g (0.11 mol) of the tricyclic ketones of the formulae(IIa, IIb, IIc) (97%) and 1.5 g of K₂CO₃ were placed in a flask at roomtemperature. The suspension was stirred at 290-300° C. for 8 hours. Thereaction mixture was cooled to 90° C., admixed with 200 ml of heptaneand a work-up as described in example 3 was carried out.

This gave a crude product having the following composition:2,6-diphenylphenol: 47.3%, tricyclic ketones of the formulae (IIa, IIb,IIc): 5.8% (in each case in GC-% by weight) and α-phenyldibenzofuran:13.6 GC-% by area. The 2,6-diphenylphenol product was isolated bycrystallization from heptane in a yield of 44% (12.5 g, 99 GC-% byarea).

EXAMPLE 6

10 g of Pd/Al₂O₃ catalyst (0.72% by weight of palladium on a γ-Al₂O₃(gamma-Al₂O₃) support in the form of extrudates having a length of 4 mm)together with 30 g (0.12 mol) of the tricyclic ketones of the formulae(IIa, IIb, IIc) (97%) were placed in a flask at room temperature. Thesuspension was stirred at 290-300° C. for 8 hours. This gave a crudeproduct having the following composition: 2,6-diphenylphenol: 25.7%,tricyclic ketones of the formulae (IIa, IIb, IIc): 10.3% (in each casein GC-% by weight) and 2-cyclohexyl-6-phenylphenol: 34.6 GC-% by area.

EXAMPLE 7

0.24 g of 5% Pd/C catalyst and 15 g (0.06 mol) of the tricyclic ketonesof the formulae (IIa, IIb, IIc) (97%) were placed in a flask at roomtemperature. The suspension was stirred at 290-300° C. for 2 hours. Thesuspension was cooled and, at 25° C., diluted with 50 ml of acetone. Thecatalyst was filtered off and the crude product was evaporated on arotary evaporator. The 2,6-diphenylphenol product was subsequentlyisolated by two-stage crystallization of the crude product (13 g) fromheptane/isopropanoll (25:1) in a yield of 50% (7 g, 99 GC-% by area).

EXAMPLE 8

13.3 g of Pd/Al₂O₃ (from example 5) together with 30 g (0.11 mol) of thetricyclic ketones of the formulae (IIa, IIb, IIc) (97%) were placed in aflask at room temperature. The suspension was stirred at 295° C. for 8hours. The reaction mixture was cooled to 60° C. and then admixed with200 ml of heptane and a work-up as described in example 3 was carriedout. The catalyst which had been separated off was reused for the nextdehydrogenation reaction.

This gave a crude product (24.5 g) having the following composition:2,6-diphenylphenol: 54.3%, tricyclic ketones of the formulae (IIa, IIb,IIc): 8.2% (in each case in GC-% by weight) and2-cyclohexyl-6-phenylphenol: 6.9 GC-% by area and α-phenyldibenzofuran:6.3 GC-% by area.

EXAMPLE 9 Synthesis of 4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol)

61.5 g (0.25 mol) of 2,6-diphenylphenol and 875 g of methanesulfonicacid (100%) were placed in a flask. 15.4 g (0.14 mol) of1,1,1-trifluoroacetone were subsequently added at 20° C. To complete thereaction, the suspension was stirred at 45° C. for 10 hours. Thesuspension was subsequently cooled to 20° C. and filtered. Thefiltercake was washed with distilled water (730 g each time) untilneutral and dried. This gave 71 g (97% of theory) of4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol) in the formof a white powder (HPLC-% by weight: 98%).

EXAMPLE 10

325 g (1.31 mol) of 2,6-diphenylphenol (99%) and 2400 g ofmethanesulfonic acid (100%) were placed in a double-walled reactor at20° C. The suspension was admixed with 81.3 g (0.73 mol) of1,1,1-trifluoroacetone and stirred at 50° C. for 10 hours. After thereaction was complete, the suspension was admixed with 4200 g of tolueneand the reaction mixture was stirred at 50° C. for 30 minutes. Thephases were separated at 50° C. and the toluene phase was washed with1680 g of water, 1680 g of 2% strength sodium carbonate solution and1680 g of water. The solvent toluene was distilled off. This gave 376 g(95% of theory) of4,4′-[1-(trifluoromethyl)ethylidene]bis(2,6-diphenylphenol) in the formof a white powder (HPLC-% by weight: 97%).

The invention claimed is:
 1. A process for preparing4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenols) of theformula (I)

where the radical R is unbranched or branched C₁-C₆-alkyl orC₁-C₆-perfluoroalkyl, which comprises the process steps a) reaction ofcyclohexanone in the presence of a basic catalyst to form a reactionmixture comprising the tricyclic condensation products of the formula(IIa), (IIb) and/or (IIc)

and water, b) separation of a mixture of the tricyclic condensationproducts comprising the compounds of the formulae (IIa), (IIb) and/or(IIc) from the reaction mixture formed in step a), c) dehydrogenation ofthe tricyclic condensation products comprising the compounds of theformulae (IIa), (IIb) and/or (IIc) obtained in step b) in the presenceof a Al₂O₃ supported transition metal Pd catalyst, and carbonates ofalkali metals or alkaline earth metals, in the condensed phase to form areaction mixture comprising 2,6-diphenylphenol of the formula (III),

d) separation of 2,6-diphenylphenol of the formula (III) from thereaction mixture formed in step c) and e) reaction of the2,6-diphenylphenol of the formula (III) obtained in step d) with atrifluoromethyl ketone of the formula (IV)

where the radical R is as defined for formula (I), in the presence of astrong organic acid to form the4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenol) of theformula (I).
 2. The process of claim 1, wherein an aqueous solution ofan alkali metal hydroxide or alkaline earth metal hydroxide is used asbasic catalyst in step a).
 3. The process of claim 1, wherein an aqueoussolution of sodium hydroxide is used as basic catalyst in step a). 4.The process of claim 1, wherein the reaction according to step a) iscarried out at a temperature in the range from 90 to 180° C.
 5. Theprocess of claim 1, wherein the reaction according to process step a) iscarried out in the presence of a solvent or solvent mixture which formsan azeotrope with water.
 6. The process of claim 5, wherein the waterformed in step a) is separated from the reaction mixture by distillationin the form of an azeotrope with the solvent or solvent mixture usedduring the reaction.
 7. The process of claim 5, wherein xylene, tolueneor ethylbenzene or a mixture thereof is used as solvent.
 8. The processof claim 1, wherein the separation according to process step b) iscarried out in the form of a distillation.
 9. The process of claim 1,wherein the dehydrogenation according to process step c) is carried outin the presence of a catalyst comprising palladium and/or platinum on asupport.
 10. The process of claim 1, wherein the dehydrogenationaccording to process step c) is carried out in the presence of a Pdcatalyst supported on Al₂O₃ or a carbon support.
 11. The process ofclaim 1, wherein the dehydrogenation according to process step c) iscarried out in the presence of hydroxides or carbonates of alkali metalsor alkaline earth metals.
 12. The process of claim 1, wherein theisolation of 2,6-diphenylphenol according to process step d) is carriedout in the form of a crystallization.
 13. The process of claim 1,wherein the reaction according to process step e) is carried out at atemperature in the range from 10 to 60° C.
 14. The process of claim 1,wherein the reaction according to process step e) is carried out in thepresence of an organic acid having a pKa of up to
 2. 15. The process ofclaim 1, wherein the reaction according to process step e) is carriedout in the presence of methanesulfonic acid.
 16. The process of claim 1,wherein 2,6-diphenylphenol and the trifluoromethyl ketone of the formula(IV) are used in a molar ratio of from 1:1 to 2:1 in process step e).17. The process of claim 1, wherein the radical R is methyl ortrifluoromethyl.
 18. The process of claim 1, wherein the radical R ismethyl.
 19. The process of claim 1, wherein the4,4′-[1-(trifluoromethyl)alkylidene]bis(2,6-diphenylphenol) of theformula (I) formed in process step e) is separated off from theresulting reaction mixture by extraction.
 20. A process for preparing2,6-diphenylphenol of the formula (III)

which comprises the steps i) reaction of cyclohexanone in the presenceof a basic catalyst to form a reaction mixture comprising the tricycliccondensation products of the formula (IIa), (IIb) and/or (IIc)

and water in the presence of a solvent or solvent mixture other thancyclohexanone which forms an azeotrope with water, with the water formedbeing separated off from the reaction mixture by distillation in theform of an azeotrope with the solvent or solvent mixture used during thereaction, ii) separation of a mixture of the tricyclic condensationproducts of the formulae (IIa), (IIb) and/or (IIc) from the reactionmixture formed in step i) and iii) dehydrogenation of the tricycliccondensation products comprising the compounds of the formulae (IIa),(IIb) and/or (IIc) obtained in step ii) in the presence of a Al₂O₃supported transition metal Pd catalyst, and carbonates of alkali metalsor alkaline earth metals, in the condensed phase to form a reactionmixture comprising 2,6-diphenylphenol of the formula (III)


21. A process for dehydrogenating compounds of formula (IIa), (IIb),and/or (IIc)

in the presence of an Al₂O₃ supported Pd catalyst, and carbonates ofalkali metals, in the condensed phase to form a reaction mixturecomprising 2,6-diphenylphenol of formula (III),


22. The process of claim 21, further comprising separating the supportedPd catalyst from the reaction mixture and reuse the catalyst for atleast four times in subsequent dehydrogenation processes of compounds offormula (IIa), (IIb), and/or (IIc) without appreciable decreases inactivity or selectivity.
 23. The process of claim 1, further comprisingseparating the supported Pd catalyst from the reaction mixture and reusethe catalyst for at least four times in subsequent dehydrogenationprocesses of compounds of formula (IIa), (IIb), and/or (IIc) withoutappreciable decreases in activity or selectivity.
 24. The process ofclaim 20, further comprising separating the supported Pd catalyst fromthe reaction mixture and reuse the catalyst for at least four times insubsequent dehydrogenation processes of compounds of formula (IIa),(IIb), and/or (IIc) without appreciable decreases in activity orselectivity.